(a) Field of the Invention
The present invention relates to a motor drive system. More particularly, the present invention relates to a motor drive system for a CD-ROM spindle motor, the motor drive system having a variable gain.
(b) Description of the Related Art
A three-phase BLDC (brushless direct current) motor is generally used as the spindle motor in a CD-ROM. An output torque of the BLDC motor is proportional to a current flowing to a motor load. To control rpm, the spindle motor includes a system that frequently detects an output current such that the output current can be controlled to a level proportional to an input control voltage.